There exists a need for a pendent type sprinkler head specifically designed to meet the special discharge requirements of residential, automatic, fire-protection sprinkler systems. The special discharge requirements for residential sprinklers are the result of: limited water pressures available for the system; the need to provide coverage, in the case of smaller rooms, with only one sprinkler; and the desire to generate a high percentage of relatively large water drops in the spray.
The water supply to industrial and commercial sprinkler systems is generally fed through relatively large diameter pipes (i.e., 4 inches or greater), and so there are minimal friction losses between the city main and the sprinkler system. In other cases where the available pressure is limited, high-flow producing fire pumps are often used. In residential applications, however, the domestic water supply from the street main is generally fed thru relatively small diameter pipes (i.e. 11/2 inches or less) and the emphasis on low cost typically prohibits the use of high-flow pumps. The National Fire Protection Association has indicated that residential sprinkler systems must be designed to help protect against injury, loss of life, and property damage, with as little as 26 gallons per minute (gpm) flow. This criteria limits the number of sprinklers that can effectively discharge in the event of a fire. For the case of a large room (e.g., 14 ft. by 28 ft. and containing four sprinklers), preferably only two of the sprinklers should discharge (i.e. at 13 gpm per sprinkler). Because of this and because only one sprinkler will be called upon to protect a smaller room (e.g. 12 ft. by 12 ft.), a residential sprinkler must provide a much more uniform spray pattern over its entire design area, than is the case for state-of-the-art pendent sprinklers previously developed for industrial/commercial applications.
In order to improve the chance for occupants to escape or be evacuated, a residential sprinkler must prevent or delay flashover (i.e., uncontrolled spread of the fire). This necessitates controlling a fire in its early stages. Furnishings employing petroleum based materials (e.g., synthetic fibers) are a particular problem in this regard since they can result in fast-developing, high-heat output fires. Relatively large water drops are required to penetrate the updrafts and reach the base of this type of fire. Conventional industrial/commercial pendent sprinklers operating with flow-pressure characteristics equivalent to that required in residential applications, produce a higher percentage of small-atomized water drops than that desired in the residential case.
Prior patent applications of Grinnell Fire Protection Systems Company, Inc. have also concerned a residential sprinkler head. Fischer et al. Ser. No. 34,686 concerns an improved fusible link for reducing response time; Fischer et al. Ser. No. 53,262 now U.S. Pat. No. 4,279,309 discloses a non-circular throat for improving spray uniformity. The subject of both applications are employed in embodiments of the present invention and are herein incorporated by reference.